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2014 The Bad Science Show - Melbourne School Shows & School Incursions

The Vanishing Ball and Predictive Pathways


To explain the limitations of the human eye and how the brain makes up for these short comings. 

The Trick

In Deceptology, I threw a ball in the air that appeared to vanish in mid-air. Not matter how closely the audience followed the ball's path, they just could keep up with where the ball was or even how many balls were there.

The Explanation

There are several ways to vanish a small object like a ball. It is easier to start with a coin when practicing. Hold the coin in the palm of your right hand. Reach over with your left hand and pretend to take the coin. Drop your right hand by your side as your left hand moves away.

Keep your eye on the imaginary coin as you pretend to throw it in the air. You can then reach into your pocket with right hand and "find" the coin.  

So why do we see the coin vanish in midair when it never left my right hand?

Because of 'predictive errors.'

Our brain takes time to the process information it takes in. This means that there is a tiny delay between an event happening and us experiencing it. That delay can be us short as 13ms and as long as 15 seconds. 

So when I throw the ball up and down, it is actually further along it's path than you perceive it.  Your brain makes up for this delay by guessing when an object should be, rather than where it is. You've heard of living in the present, predicting in the future. Well your brain is living in the past trying to predict the present.

​And sometimes, your brain makes a mistake. We call these 'predictive errors.' You brain predicts that you should see a ball...and so it shows you one. 

​Psychologist Gustav Kuhn found that 2 out of 3 people experience the ball vanishing in mid air. This number was even higher when he really threw the ball in the air first to teach the participants brain what to expect.

​Have you ever pretended to throw a chip for a seagull only to have it chase after the imaginary food? Your brain is doing the same thing, trying to predict the path of an object that isn't there?


Grab a loaf of bread and head outside. Look for a nearby flock of seagulls or a kit of pigeons (bet you didn't know that the collective noun for pigeons is "kit."

Now feed the birds like a nana with too much time on her hands. 

Can you trick the birds into believing you are throwing bread when you are not?

What technique fools the most birds?

Do the the birds learn the difference between a fake throw and real throw?

What is the difference between feeding birds and the throwing ball illusion?


Further Reading
Tricking The Brain: How Magic Works

Nicholas J. Johnson


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